oh, i'm sorry, i guess i'd misunderstood your problem.

$old_db="emdb1";
$new_db="kuku"; 
$string="AUTHORIZATION,libctl62-m.sl,CONTROLM,emdb1,b02ed6600206ca161d
+165355c67b72073b6123d6838f1f68203b78cb9c4c63c9,emdb2,,;" ; 
$string =~ s/$old_db/$new_db/g;
print $string;
[download]

does it work properly now?!
=)